The present invention relates generally to a system for controlling the occurence of detonation in internal combustion engines. More particularly, the present invention relates to a system which evaluates the suitability of the octane rating of the fuel used in a vehicle and makes comparative recommendations regarding the octane rating of fuel to be used.
In his 1964 book, "My Years With General Motors", Alfred P. Sloan wrote, "The central problem in automotive engineering has been to develop a more satisfactory relationship between the fuel and the engine." Since that time, considerable progress has been made in solving this problem. For example, applicant's U.S. Pat. No. 4,116,173 teaches the use of an accelerometer as an engine detonation sensor to distinguish detonation in individual cylinders of an engine, and to retard spark advance to those cylinders of the engine which are detonating. This scheme is currently being implemented using digital computers and is capable of making an engine somewhat adaptive to the octane rating of the fuel supplied to the engine.
A further improvement in the development of an engine that can adapt to fuel with different octane ratings may be found in U.S. Pat. No. 4,594,982, issued on June 17, 1986 to A. Takahashi et al., in U.S. Pat. No. 4,594,983, issued on June 17, 1986 to A. Takahashi et al., in U.S. Pat. No. 4,619,236, issued on Oct. 28, 1986 to T. Okada et al., in U.S. Pat. No. 4,630,584, issued on Dec. 23, 1986 to K. Higashiyaha et al., in U.S. Pat. No. 4,635,604, issued on Jan. 13, 1987 to T. Iwata et al. These five inventions utilize the occurance of engine detonation to indicate to the detonation control system the type of gasoline in use and thus permit the detonation control system to more optimally adapt its functioning to that type of gasoline.
It will be appreciated that there are performance tradeoffs to consider when controlling engine detonation. As a very rough rule of thumb, in the range between 1 and 10 degrees of detonation control system spark retard, each degree is worth one octane number in its capability to suppress detonation. However, each degree costs a 1% loss of engine torque. Beyond the first 10 degrees of such retard, the torque curves become steeper and the torque loss per degree becomes greater.
Because of the steep torque loss curve beyond 10 degrees, there is a practical lower limit to the range of fuel octane numbers over which an engine can be made self-adaptive. In modern electronic detonation control systems, this range is accounted for by limiting the range of authority over which the control system is permitted to retard spark advance in order to suppress detonation. See, for example, Meyer, "Austin-Rover Montego Programmed Ignition System", SAE Paper 841293. This paper describes British Leyland's Austin-Rover Montego programmed ignition system as having "a maximum correction of 20 degrees".
In practice, as long as the owner of an automobile uses fuel whose octane is above the lower limit which can be accommodated by the control system, the engine will automatically adapt and run without destructive detonation. If an owner supplies his vehicle with fuel which has an octane rating higher than necessary, the retard authority of his electronic detonation control system will seldom be invoked. It should be noted that the ideal octane rating will vary among different drivers because of differing driving habits, and differing attitudes regarding economy vs. performance.
Whatever the ideal octane rating is, the use of an excessively high octane fuel results in a needless economic penalty. The present incremental retail cost of an octane number as posted on gasoline filling station pumps is approximately five cents per octane number per gallon. When multiplied by the annual U.S. gasoline consumption of roughly one hundred billion gallons, five cents per octane number per gallon results in a national yearly cost of five billion dollars for each incremental octane number. Thus, there will be considerable economic waste if, nationwide, a fuel of only a slightly higher octane number than necessary is used. To further illustrate the economic importance of vehicle fuel expenditures, it should be noted that a recent national survey of household expenditures reported that, on average, household cost for vehicle fuel exceeded the total cost of all other household purchases of energy.
The vehicle owner, because he selects what fuel to use, could play an important role in preventing needless economic waste and in achieving a better relationship between the engine and the fuel. Currently, automobile manufacturers may print the value of recommended fuel octane number in owner's manuals for each model automobile. Unfortunately, this recommendation falls short of providing optimal guidance to the owner for a number of reasons. For example, when an automobile is driven on hilly roads or is used to pull a trailer, the automobile requires a higher octane fuel than it would in ordinary driving. Also, vehicles supposedly identical in design and construction have significant differences in their octane requirements. Moreover, octane requirement frequently increase with mileage as combustion chamber deposits accumulate and change with engine wear. For example, in Alquist "Some Observations of Factors Affecting ORI", SAE Paper No. 750932, it is reported that a difference of up to 6.9 octane numbers in initial octane requirement is observed when different (supposedly identical) cylinder head sets are used on the same clean V-8 engine.
Also, in Betts, "Improved Fuel Economy by Better Utilization of Available Octane Quality", SAE Paper 790940, the author reports that compression ratios varied by up to 1.5 compression ratios between examples of the same model engine, and that cylinders in the same engine varied by up to 1 compression ratio. These compression ratio variations directly affect the octane requirement of an engine. Further, Graiff, "Some New Aspects of Deposit Effects on Engine Octane Requirement Increase and Fuel Economy", SAE Paper 790938, reports a 13 octane number spread in the requirements of the individual cylinders of the same engine following about 200 hours of deposit accumulation.
Thus, it would be desirable to provide a means for advising the vehicle owner of desirable changes in the octane of the fuel which he has been using. This would not only improve the performance of his engine, but could also save the individual and the nation the needless expense of using excessively high octane fuel. This would require an intelligent, dynamic and personalized octane requirement computation which is tailored to an individual engine, its operational environment, and to individual driving habits.
Accordingly, it is a principal object of this invention to provide a system for an automobile that will help the driver optimize the octane rating of the fuel used by recommending desirable changes in the fuel octane rating.
It is also an object of this invention to prevent premature automobile engine wear and damage, by providing a system which will request a higher octane fuel when the octane of the fuel which has recently been consumed from the vehicle's tank is too low.
It is another object of this invention to provide a system for an automobile that will request a lower octane fuel when the prevailing octane of the fuel which has recently been consumed from the vehicle's tank is too high, and to thereby optimize dollar fuel economy.
It is an additional object of this invention to provide a system that will indicate to the driver when the prevailing octane grade of fuel which has recently been consumed from the vehicle's tank is generally correct.
It is also an object of this invention to provide a system that will automatically make recommendations regarding the correct octane fuel taking into account such factors as driver habits, vehicle loading, engine wear, combustion chamber deposits, and the many other factors influencing engine octane requirement.